The present invention relates to a seat belt apparatus including a seat belt retractor with a lock mechanism capable of engaging a pawl member with a pawl wheel to thereby lock or prevent a bobbin with a webbing wound thereon from rotating in the webbing pay-out direction thereof.
A seat belt apparatus for holding the occupant of a vehicle on a seat in safety comprises a webbing, a buckle, a mounting device, and a retractor for a seat belt (which is also referred herein to as a seat belt retractor).
The seat belt retractor is a winding device which not only, when the seat belt is not in use, automatically takes up the webbing to thereby prevent the webbing against damage and but also, when the seat belt is in use, is capable of changing the length of the webbing freely.
As the seat belt retractor of this type, generally, there is used a seat belt retractor including an emergency lock mechanism structured such that it can physically lock the pay-out of the webbing according to the action of inertia sensing means capable of reacting to sudden acceleration, a collision, or sudden deceleration, whereby the seat belt retractor is able to restrict the occupant effectively and safely using the thus-structured emergency lock mechanism.
And, as the emergency lock mechanism of this type, there is spread a lock mechanism structured such that, in case where the acceleration of the vehicle or the pay-out acceleration of the webbing is equal to or greater than a given level, a pawl member is engaged with a pawl wheel to thereby be able to lock or prevent a bobbin with the webbing wound thereon against rotation in the webbing pay-out direction thereof.
Now, FIGS. 12 and 13 show a conventional example of a pawl wheel used in the lock mechanism of this type.
A pawl wheel 1, which is shown in FIG. 12, has a structure that ratchet teeth 1a to be engaged with the pawl member are formed in the inner peripheral portion thereof at regular intervals.
Also, a pawl wheel 3, which is shown in FIG. 13, is structured such that ratchet teeth 3a to be engaged with the pawl member are formed in the outer peripheral portion thereof at regular intervals.
By the way, in the case of an emergency lock mechanism using a pawl wheel, generally, for example, in case where the pay-out acceleration of the webbing exceeds 2.0 G, the pawl member an be engaged with the pawl wheel.
However, on the webbing that has been played out from the retractor, there is applied the urging force of a winding spring disposed on the retractor. Therefore, when stopping the mounting of the seat belt, in case where the webbing is wound vigorously with all urging force of the winding spring, the winding of the webbing is executed at a fairly quick speed. Thus, due to a reaction to the impact of the webbing when it is wound fully, in a winding shaft, there is instantaneously generated rotation acceleration going in the webbing pay-out direction. The acceleration, which is generated in this case, can exceed the operation standard value of the lock mechanism, that is, 2.0 G. In such case, there is high occurrence probability of an end lock phenomenon, that is, a phenomenon in which the pawl member of the lock mechanism can be engaged with the pawl wheel to thereby prevent the webbing, in a state where the webbing is wound fully, from being played out.
And, in case where such end lock phenomenon occurs, to remove it, there is necessary a lock removal operation in which, for example, the full-wound webbing is forcibly played out once and the thus slightly played-out webbing is returned to thereby remove the locked condition of the webbing, which results in a poor operation efficiency.
Also, in the above-mentioned conventional pawl wheels 1, 3, the plurality of ratchet teeth 1a, 3a, which are respectively arranged along the peripheral directions of the respective pawl wheels, are the same in dimension; and, all of the ratchet teeth are arranged on a single addendum circle 1b or 3b. Therefore, when any one of the ratchet teeth is engaged with the pawl member, there is obtained firm engagement. This means that, when removing the end lock phenomenon, it is difficult to remove the engagement between the ratchet tooth and pawl member at any engaged position.
In view of the above, the present invention aims at solving the above-mentioned problems. Accordingly, it is an object of the invention to provide a seat belt apparatus including a seat belt retractor with a lock mechanism, structured such that, when removing the mounting of the webbing, even in case where the webbing is returned with great force, there can be reduced the possibility of occurrence of the end lock phenomenon and, even in case where the end lock phenomenon occurs, the removal of such end lock phenomenon can be facilitated, thereby being able to improve the lowered operation efficiency due to the occurrence of the end lock phenomenon.
In attaining the above object, according to the invention, there is provided a seat belt apparatus including a seat belt retractor with a lock mechanism structured such that, when the acceleration of a vehicle or the pay-out acceleration of a webbing is equal to or greater than a predetermined value, a pawl member can be engaged with a pawl wheel to thereby lock the rotation of a bobbin with the webbing wound thereon in the webbing pay-out direction thereof, wherein the pawl wheel is structured such that two or more kinds of ratchet teeth differing in addendum circle diameter are mixedly arranged in the peripheral direction of the pawl wheel according to a predetermined manner.
In the above structure, when the vehicle acceleration or the webbing pay-out acceleration is equal to or greater than a predetermined value, the pawl member forming the lock mechanism gets into motion such as rotary motion for engagement with the pawl wheel, while the motion of the pawl member varies according to the acceleration applied thereto; for example, when the acceleration applied is small, the motion of the pawl member is also small.
Generally, the webbing pay-out acceleration to be instantaneously applied to the winding shaft due to reaction to the impact given when the webbing is wound back up to its terminal end in removing the mounting of the webbing, and the vehicle acceleration to be detected by a vehicle acceleration sensor when the door of the vehicle is closed with great force, normally, correspond to the value that exceeds the standard value of the operation of the lock mechanism; however, when compared with the acceleration to be generated in the actual vehicle collision, they are rather small.
And, in case where the pawl member carries out engaging motion with respect to the pawl wheel through the action of such small acceleration, in the case of the above structure, the ratchet teeth to be arranged on the pawl wheel are composed of two or more kinds of ratchet teeth differing in addendum circular diameter; and, therefore, for example, in case where the internal teeth or ratchet teeth to be engaged with the pawl member are structured such that the addendum circle diameter thereof is set larger than the standard one, the pawl member is not be able to reach such ratchet teeth, with the result that their engagement cannot be attained. Also, even when the pawl member is engaged with the pawl wheel to thereby put the webbing into a locked condition, as described above, in case where the internal teeth or ratchet teeth to be engaged with the pawl member are structured such that the addendum circle diameter thereof is set larger than the standard one, since the engagement between the pawl member and the ratchet tooth to be engaged therewith is shallow, a webbing operation force and a webbing operating quantity necessary to remove such webbing locked condition can be reduced when compared with the conventional structure.
That is, according to the above structure, when removing the mounting of the webbing, even in case where the webbing is returned with great force, there can be reduced the possibility of the end lock phenomenon occurring; and, even in case where the end lock phenomenon occurs, there can be enhanced the possibility that the removal of the end lock phenomenon can be facilitated, thereby being able to improve the lowered operation efficiency caused by the end lock phenomenon.
Further, in case where the retractor includes a pre-tensioner, in a locking operation to be executed after the pre-tensioner is operated, the webbing pay-out acceleration to be input rises suddenly, thereby raising a fear that the extension quantity of the webbing can be increased. Therefore, to control the webbing extension quantity down to a small value, preferably, the locking operation maybe execute data nearly stage. According to the above structure, when a sufficiently large level of acceleration is applied in this manner, the pawl member can be engaged with any one of the ratchet teeth, so that the occupant can be restricted positively without increasing the webbing extension quantity.